Digestion in treatment of wastewater is a key process for the reduction of bio-solids and pathogen counts prior to any solids disposal. Most wastewater treatment plants employ some kind of digestion process with aerobic digestion of sludge becoming increasingly popular, in contrast to anaerobic digestion.
Aerobic sludge digestion is one process that may be used to reduce both the organic content and the volume of the sludge. Under aerobic conditions, a large portion of the organic matter in sludge may be oxidized biologically by microorganisms to carbon dioxide and water. The process generally results in approximately 50% reduction in solids content. Aerobic sludge digestion facilities may be designed for either batch or continuous flow operations.
Aerobic digestion of sludge is increasingly preferred over anaerobic digestion as it enables an improved dewatering process, better sludge stability, reduced on-site tankage requirements, and generally less offensive odors. Moreover, aerobic sludge digestion provides cost and performance advantages over other conventional methods of reducing sludge including lower capital costs, ease of operation, and system reliability.
Unfortunately, conventional air-based aerobic sludge digestion systems tend to have higher operating costs mainly attributable to the consumption of excessive amounts of power, on average about 1500 hp per million gallons of treated material. This high power demand is generally due to the highly viscous nature of digested liquor and the low mass transfer achieved when using conventional jet aerators or air diffuser systems.
What is needed therefore is an energy efficient method and system for aerobic sludge digestion in wastewater treatment plants.